All the surprises at the Aussie Open are almost the direct result of the fact that players have just finished their offseason training and some players have improved more than others during the offseason.

Players often use the "off season" to reinvent themselves, be it physically, mentally, or technically. Many of them have had a chance to implement new coaching staff and approaches. Accordingly, their confidence is at an all-time high. The losses haven't started piling up, and there's no source of disbelief. Their opponents, on the other hand, are often quite taken aback. It's a perfect storm for "hot" players.

It helps that the AO, especially before it switched to plexi-pushin', probably best accommodates modern players. And as the first major, players are at their freshest for the event. It's probably why it seems to host the most thrillers.